Electromagnet-controlling system

ABSTRACT

An arrangement for feeding the power winding of an electromagnet with rectified A.C. by means of a thyristor or triac. The latter is inserted in parallel with a transistor the conducting condition of which is provided by a condenser fed by the rectified A.C. and discharging into the base of the transistor which latter acts then on the electrode controlling the thyristor, to allow the latter to return into its non-conductive condition at the end of an alternation. A maintenance or holding current is provided either through an auxiliary electromagnet winding or through a chopped current feeding the power winding and produced by a pulse generator.

United States Patent 91 Stampfli [54] ELECTROMAGNET-CONTROLLING SYSTEM[75] Inventor: Harald Stampfli,

Geneva, Switzerland Petit-Saconex,

[73] Assignee: Lucifer S. A., Carouge-Geneva,

Switzerland [22] Filed: Apr. 4, 1972 [21] Appl. No.: 240,354

[30] 7 Foreign Application Priority Data Apr. 23, 1971 Switzerland..'.....59()9/71 June 4,1971 Germany ..P 21 28 651.1

[5 6] References Cited UNITED STATES PATENTS Gieffers ..3 l 7/DIG. 4Lancles ..3l7/l48.5 B

[111 3,737,736 51 June 5,1973

Primary ExaminerWilliam H. Beha, Jr. Att0rneyEmory L. Groff et a1.

57 ABSTRACT An arrangement for feeding the power winding of anelectromagnet with rectified A.C. by means of a thyristor or triac. Thelatter is inserted in parallel with a transistor the conductingcondition of which is pro vided by a condenser fed by the rectified A.C.and discharging into the base of the transistor which latter acts thenon the electrode controlling the thyristor, to allow the latter toreturn into its non-conductive condition at the end of an alternation. Amaintenance or holding current is provided either through an auxiliaryelectromagnet winding or through a chopped current feeding the powerwinding and produced by a pulse generator.

5 Claims, 2 Drawing Figures ELECTROMAGNET-CONTROLLING SYSTEM The presentinvention covers an arrangement controlling an electromagnet and adaptedto supply upon energization a strong initial current, followed by aweaker maintenance current. Such an arrangement allows in particular theelectromagnet to exert a larger initial attraction without exaggeratedlyheating its winding, since the maintenance current following the initialcurrent is comparatively weak.

The control arrangement comprises, according to the invention, a Graetzrectifier connected with a supply of AC. and feeding an electromagnetwinding in series with a thyristor, the control electrode and thecathode of which are connected with each other through delaying meanswhich become conductive at a predetermined moment following the closingof a control switch.

In the accompanying drawings:

FIGS. 1 and 2 illustrate diagrammatically and by way of example twoembodiments of the arrangement forming the object of the invention.

As illustrated in FIG. 1, a rectifier 1 operating on both alternationsis connected through a switch S with the terminals a and b fed by asupply of A.C., e.g. the

mains.

The controlled electromagnet includes two windings B, and B themaintenance winding B being fed directly across the terminals and d ofthe rectifier l. The power winding B, is connected across said outputterminals of the rectifier, in series with a resistance R and atransistor T,. Said winding B, is also connected with the negativeoutput terminal d of the rectifier through a thyristor T in series withtwo diodes D, and D The base of the transistor T, is connected with acondenser C through a Zener diode Z. This condenser C forms with theresistance R, and RC element. The base of the transistor T, is connectedwith its emitter through a leak resistance R The power winding B, isshunted by a diode D The operation of the arrangement is as follows:

The closing of the switch S obviously energizes the winding B Thewinding B, is also subjected to a positive voltage since the transistorT, is non-conductive at the start; in fact the control electrode of thethyristor T is practically subjected to the voltage of the positiveterminal c of the rectifier, whereas the cathode of said thyristor issubstantially at the voltage of the terminal d. The thyristor T istherefore conductive, so that the power winding B, is fed.

The condenser C is loaded gradually through the resistance R, and whenitsvoltage reaches the threshold voltage of the Zener diode, saidvoltage is applied on the base of the transistor T, which becomesconductive.

The control electrode of the thyristor T returns then to the voltage ofthe terminal b and is therefore negative with reference to the cathodeof the thyristor by reason of the drop in voltage by about 2 voltsacross the diodes D, and D Since the drop in voltage across thetransistor T, is about 0.5 V,.the control electrode is biased negativelyby about 1.5 V with reference to the cathode of the thyristor T Thethyristor is therefore under conditions which make its extinction aneasy matter during the next passage through zero of the rectifiedcurrent fed by the rectifier l.

After extinction of the thyristor T the winding B, is no longer fed andonly the maintenance winding B remains operative. It should be remarkedthat the diode D cuts out all overvoltages in the winding B, during saidextinction of the thyristor T Of course, many modifications may bebrought to the circuit described and in particular it is possible to replace the Zener diode Z by any other component provided with a thresholdvoltage beyond which it becomes conductive.

The embodiment illustrated in FIG. 2 distinguishes from the firstembodiment through the absence of an auxiliary maintenance winding B forthe electromagnet. The circuit feeding the winding B, is identical withthat of FIG. 1 except for a resistance R inserted be tween the collectorof the transistor T, and the control electrode of the thyristor T Inthis second embodiment, a pulse generator 2 provides the application tothe control electrode of the thyristor T of pulses synchronized with thefrequency of the mains and phase-shifted with reference to the latter.Thus, when the transistor T, becomes conductive and preventsconsequently the automatic ignition of the thyristor T the latter isrendered conductive during each alternation by the pulses supplied bythe generator 2. Thus, there is obtained a chopped current, the averagevalue of which is lower than that of the current obtained at the start.Said chopped current forms the maintenance current for theelectromagnet.

The pulse generator comprises, as well-known per se, a single-junctiontransistor T fed through a resistance R, and across a Zener diode Z Thevoltage across the terminals of said diode Z is applied to the base ofthe transistor T through a resistance R which loads a condenser C Eachtime the voltage across the terminals of said condenser reaches thethreshold value of the transistor T the latter becomes conductive andallows the passage through a resistance R, of a current which produces avoltage pulse which is applied to the control electrode of the thyristorT An important advantage of the circuits described resides in the factthat, whatever the voltage of the mains may be, the voltage to which thetransistor T, is subjected never rises above a few volts, since foravoltage of this magnitude, the thyristor T becomes immediatelyconductive.

It is of course possible to bring numerous modifications to the wiringdiagrams described and, in particular, the thyristor T may be replacedby a triac. In such a case, the pulse generator 2 may be provided so asto supply pulses of a negative polarity while the diodes B,v I"

and D may be omitted.

I claim:

1. An electromagnet-controlling system adapted to produce a strongstarting current for an electromagnet power winding followed by a weakerholding current comprising a Graetz rectifier, adapted to be fed withA.C., a thyristor circuit including an anode and a cathode inserted inseries between the rectifier and the electromagnet power winding and acontrolling electrode, and delaying means inserted between said cathodeand controlling electrode and adapted to become conductive at apredetermined moment after energization of the rectifier to allow thethyristor circuit to return to its inoperative condition and meansfeeding a weaker holding current to the electromagnet.

2. A system as claimed in claim 1, wherein the delaying means include atransistor, the emitter-collector circuit of which is inserted inparallel with the thyristor circuit and is connected with thecontrolling resistance of the latter, a resistance and condenser circuitfed by the rectifier and an element provided with a threshold voltageand operatively connecting said condenser with the transistor base assoon as the condenser voltage has reached a predetermined voltage.

3. A system as claimed in claim 1, wherein the delaying means include atransistor, the emitter-collector circuit of which is inserted inparallel with the thyristor circuit and is connected with thecontrolling resistance of the latter, a resistance and condenser circuitfed by the rectifier and an element provided with a threshold voltageand operatively connecting said condenser with the transistor base assoon as the condenser voltage has reached a predetermined voltage, andat least one diode inserted between the negative terminal of therectifier and the cathode of the thyristor circuit and leading thecurrent passing out of the latter towards voltage and operativelyconnecting said condenser with the transistor base as soon as thecondenser voltage has reached a predetermined voltage and wherein themeans feeding the holding current include a generator of pulsessynchronized with the frequency of the AC. fed to the rectifier andphase-shifted with reference thereto and means for applying said pulsesto the thyristor circuit.

1. An electromagnet-controlling system adapted to produce a strongstarting current for an electromagnet power winding followed by a weakerholding current comprising a Graetz rectifier, adaptEd to be fed withA.C., a thyristor circuit including an anode and a cathode inserted inseries between the rectifier and the electromagnet power winding and acontrolling electrode, and delaying means inserted between said cathodeand controlling electrode and adapted to become conductive at apredetermined moment after energization of the rectifier to allow thethyristor circuit to return to its inoperative condition and meansfeeding a weaker holding current to the electromagnet.
 2. A system asclaimed in claim 1, wherein the delaying means include a transistor, theemitter-collector circuit of which is inserted in parallel with thethyristor circuit and is connected with the controlling resistance ofthe latter, a resistance and condenser circuit fed by the rectifier andan element provided with a threshold voltage and operatively connectingsaid condenser with the transistor base as soon as the condenser voltagehas reached a predetermined voltage.
 3. A system as claimed in claim 1,wherein the delaying means include a transistor, the emitter-collectorcircuit of which is inserted in parallel with the thyristor circuit andis connected with the controlling resistance of the latter, a resistanceand condenser circuit fed by the rectifier and an element provided witha threshold voltage and operatively connecting said condenser with thetransistor base as soon as the condenser voltage has reached apredetermined voltage, and at least one diode inserted between thenegative terminal of the rectifier and the cathode of the thyristorcircuit and leading the current passing out of the latter towards saidnegative terminal.
 4. A system as claimed in claim 1, wherein the meansfeeding the holding current include an auxiliary holding windinginserted across the rectifier terminals in parallel with the powerwinding and thyristor circuit.
 5. A system as claimed in claim 1,wherein the delaying means include a transistor, the emitter-collectorcircuit of which is inserted in parallel with the thyristor circuit andis connected with the controlling resistance of the latter, a resistanceand condenser circuit fed by the rectifier and an element provided witha threshold voltage and operatively connecting said condenser with thetransistor base as soon as the condenser voltage has reached apredetermined voltage and wherein the means feeding the holding currentinclude a generator of pulses synchronized with the frequency of theA.C. fed to the rectifier and phase-shifted with reference thereto andmeans for applying said pulses to the thyristor circuit.